Polyurethanes are useful in a variety of applications. For example, polyurethane elastomers are used in automotive parts, shoe soles, and other products in which toughness, flexibility, strength, abrasion resistance, and shock-absorbing properties are required. Polyurethanes are also used in coatings and in flexible and rigid foams.
Polyurethanes, in general, are produced by the reaction of a polyisocyanate and a polyol in the presence of a catalyst. The catalyst is typically a low molecular weight tertiary amine such as triethylenediamine.
Polyurethane foams are produced through the reaction of a polyisocyanate with a polyol in the presence of various additives. One class of additives which is particularly effective as blowing agents is the chlorofluorocarbons (CFCs). CFCs vaporize as a result of the reaction exotherm during polymerization and cause the polymerizing mass to form a foam. However, the discovery that CFCs deplete ozone in the stratosphere has resulted in mandates for restricting CFC use. Therefore, more effort has gone into the development of alternatives to CFCs for forming urethane foams and water blowing has emerged as an important alternative. In this method, blowing occurs from carbon dioxide generated by the reaction of water with the polyisocyanate. Foams can be formed by a one-shot method or by formation of a prepolymer and subsequent reaction of the prepolymer with water in the presence of a catalyst to form the foam. Regardless of the method, a balance is needed between reaction of the isocyanate and the polyol (gelling) and the reaction of the isocyanate with water (blowing) in order to produce a polyurethane foam in which the cells are relatively uniform and the foam has specific properties depending on the anticipated application; for example, rigid foams, semi-rigid foams, and flexible foams.
The ability of the catalyst to selectively promote either blowing or gelling is an important consideration in selecting a catalyst for the production of a polyurethane foam with specific properties. If a catalyst promotes the blowing reaction to too high a degree, carbon dioxide will be evolved before sufficient reaction of isocyanate with polyol has occurred. The carbon dioxide will bubble out of the formulation, resulting in collapse of the foam and production of a poor quality foam. At the opposite extreme, if a catalyst promotes the gelling reaction too strongly, a substantial portion of the carbon dioxide will be evolved after a significant degree of polymerization has occurred. Again, a poor quality foam is produced; characterized by high density, broken or poorly defined cells, or other undesirable features. Frequently, a gelling catalyst and a blowing catalyst are used together to achieve the desired balance of gelling and blowing in the foam.
Tertiary amine catalysts are widely used in the production of polyurethanes. The tertiary amine catalysts accelerate both blowing (reaction of water with isocyanate to generate carbon dioxide) and gelling (reaction of polyol with isocyanate) and have been shown to be effective in balancing the blowing and gelling reactions to produce a desirable product.
The most widely used commercial catalysts for producing polyurethanes are triethylenediamine (TEDA), also called 1,4-diazabicyclo[2.2.2]octane, and its derivatives. Representative examples of patents which disclose synthesis of TEDA and substituted TEDA are: U.S. Pat. No. 3,297,701 (Brader et al, 1967), U.S. Pat. No. 3,375,252 (Yamada et al, 1968), U.S. Pat. No. 4,804,758 (Hoelderich et al, 1989), U.S. Pat. No. 5,041,548 (Sato et al, 1991), and U.S. Pat. No. 5,194,613 (King, 1993).
Low molecular weight tertiary amines, such as those described in the above patents, generally have offensive odors and many are highly volatile due to low molecular weight. Release of tertiary amines during polyurethane production may present significant safety and toxicity problems, and release of residual amines from consumer products is generally undesirable.
High molecular weight amine catalysts may possess reduced volatility and odor when compared to known lower molecular weight amines.